Polycarbonate (PC) resins are polymer resins that have superior mechanical strength, transparency, thermal stability, self-extinguishing properties, dimensional stability, and the like, and that have many uses for electrical and electronic products, vehicle components, and the like.
Because polycarbonate resins have a polymer structure that can facilitate flame retardancy, polycarbonate resins can be used as typical flame-retarding agents and easily achieve flame retardancy.
In particular, because PC resins can form char, a PC resin combined with a phosphorus-based flame-retarding agent can easily achieve flame retardancy without environmental problems. Moreover, as disclosed in U.S. Pat. No. 5,061,745, U.S. Pat. No. 5,204,394, and U.S. Pat. No. 5,674,924, compositions formed by melting and blending PC and a rubber-modified styrene-based resin (ABS resin) can further improve processiblity.
However, although PC resins and PC/ABS resins have merits in terms of high processiblity and superior impact resistance, both PC resins and PC/ABS resins have weak scratch resistance, so that products made of such PC resins or PC/ABS resins have low scratch resistance.
Polymethylmethacrylate (PMMA) resins not only have excellent scratch resistance and weather resistance, but also superior surface-glossing, bonding properties, and mechanical properties, such as tensile strength, elastic modulus, etc. PMMA resins are widely used in ornamental articles, signboards, illuminating materials, various kinds of construction materials, bonding agents, modifiers of other plastic materials, and the like.
However, PMMA resins have a lower impact resistance, compared with that of other plastic materials, and are likely to be fractured by an external impact. Moreover, because PMMA exhibits a limiting oxygen index of 17 required for continuous burning and does not form char upon combustion, it is difficult to impart flame retardancy to PMMA.
This difficulty is closely related to the easy formation of monomers as by-products of thermal decomposition, during which PMMA is sequentially subjected to chain scission followed by β-scission, as set forth in Polymer (published by Elsevier Science, LTD., Volume 44, pp. 883-894, 2003).
Therefore, when producing a flame retardant resin by blending only PC resin and PMMA resin, a large amount of a flame-retarding agent must be used due to the low flame retardancy of PMMA. If the amount of PMMA resin is reduced to ensure flame retardancy, however, it is difficult to attain superior scratch resistance.
U.S. Pat. No. 5,292,786 discloses a composition with superior weld line strength, which is formed by adding phosphoric ester as a flame-retarding agent and PMMA to PC and ABS resins. However, because the composition of the disclosure has a relatively small amount of PMMA to impart scratch resistance, and the PC and ABS resins in the composition have low scratch resistance, the composition may not have adequate scratch resistance.
Polyethylene terephthalate (PET) resins have excellent wear resistance as well as good mechanical properties and superior chemical resistance and thus can be advantageous for improving scratch resistance.
However, PET-based resins have the disadvantages of reduced flame retardancy and low notched-impact resistance.
Currently, as the appearance of housing materials becomes more and more important as the size of electrical and electronic products increases, resins are required to have scratch resistance. In addition, the use of flame retardant resins is emphasized to ensure fire safety. Furthermore, to address environmental concerns, there is an increasing interest in eliminating halogen containing substances from the resins. It is very difficult, however, to produce a resin that can meet all the requirements as described above using conventional techniques.
Therefore, there is still a need to develop a thermoplastic resin composition that can satisfy all requirements for superior scratch resistance, fire safety, and prevention of environmental problems while maintaining its mechanical properties.